/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.catalina;

/**
 * Common interface for component life cycle methods.  Catalina components
 * may implement this interface (as well as the appropriate interface(s) for
 * the functionality they support) in order to provide a consistent mechanism
 * to start and stop the component.
 * <br>
 * The valid state transitions for components that support {@link Lifecycle}
 * are:
 * <pre>
 *            start()
 *  -----------------------------
 *  |                           |
 *  | init()                    |
 * NEW ->-- INITIALIZING        |
 * | |           |              |     ------------------<-----------------------
 * | |           |auto          |     |                                        |
 * | |          \|/    start() \|/   \|/     auto          auto         stop() |
 * | |      INITIALIZED -->-- STARTING_PREP -->- STARTING -->- STARTED -->---  |
 * | |         |                                                            |  |
 * | |destroy()|                                                            |  |
 * | -->-----<--    ------------------------<--------------------------------  ^
 * |     |          |                                                          |
 * |     |         \|/          auto                 auto              start() |
 * |     |     STOPPING_PREP ---->---- STOPPING ------>----- STOPPED ----->-----
 * |    \|/                               ^                     |  ^
 * |     |               stop()           |                     |  |
 * |     |       --------------------------                     |  |
 * |     |       |                                              |  |
 * |     |       |    destroy()                       destroy() |  |
 * |     |    FAILED ---->------ DESTROYING ---<-----------------  |
 * |     |                        ^     |                          |
 * |     |     destroy()          |     |auto                      |
 * |     -------->-----------------    \|/                         |
 * |                                 DESTROYED                     |
 * |                                                               |
 * |                            stop()                             |
 * --->------------------------------>------------------------------
 *
 * Any state can transition to FAILED.
 *
 * Calling start() while a component is in states STARTING_PREP, STARTING or
 * STARTED has no effect.
 *
 * Calling start() while a component is in state NEW will cause init() to be
 * called immediately after the start() method is entered.
 *
 * Calling stop() while a component is in states STOPPING_PREP, STOPPING or
 * STOPPED has no effect.
 *
 * Calling stop() while a component is in state NEW transitions the component
 * to STOPPED. This is typically encountered when a component fails to start and
 * does not start all its sub-components. When the component is stopped, it will
 * try to stop all sub-components - even those it didn't start.
 *
 * Attempting any other transition will throw {@link LifecycleException}.
 *
 * </pre>
 * The {@link LifecycleEvent}s fired during state changes are defined in the
 * methods that trigger the changed. No {@link LifecycleEvent}s are fired if the
 * attempted transition is not valid.
 *
 * @author Craig R. McClanahan
 */
public interface Lifecycle {


	// ----------------------------------------------------- Manifest Constants

	/**
	 * The LifecycleEvent type for the "component after init" event.
	 */
	public static final String BEFORE_INIT_EVENT = "before_init";

	/**
	 * The LifecycleEvent type for the "component after init" event.
	 */
	public static final String AFTER_INIT_EVENT = "after_init";

	/**
	 * The LifecycleEvent type for the "component start" event.
	 */
	public static final String START_EVENT = "start";

	/**
	 * The LifecycleEvent type for the "component before start" event.
	 */
	public static final String BEFORE_START_EVENT = "before_start";

	/**
	 * The LifecycleEvent type for the "component after start" event.
	 */
	public static final String AFTER_START_EVENT = "after_start";

	/**
	 * The LifecycleEvent type for the "component stop" event.
	 */
	public static final String STOP_EVENT = "stop";

	/**
	 * The LifecycleEvent type for the "component before stop" event.
	 */
	public static final String BEFORE_STOP_EVENT = "before_stop";

	/**
	 * The LifecycleEvent type for the "component after stop" event.
	 */
	public static final String AFTER_STOP_EVENT = "after_stop";

	/**
	 * The LifecycleEvent type for the "component after destroy" event.
	 */
	public static final String AFTER_DESTROY_EVENT = "after_destroy";

	/**
	 * The LifecycleEvent type for the "component before destroy" event.
	 */
	public static final String BEFORE_DESTROY_EVENT = "before_destroy";

	/**
	 * The LifecycleEvent type for the "periodic" event.
	 */
	public static final String PERIODIC_EVENT = "periodic";

	/**
	 * The LifecycleEvent type for the "configure_start" event. Used by those
	 * components that use a separate component to perform configuration and
	 * need to signal when configuration should be performed - usually after
	 * {@link #BEFORE_START_EVENT} and before {@link #START_EVENT}.
	 */
	public static final String CONFIGURE_START_EVENT = "configure_start";

	/**
	 * The LifecycleEvent type for the "configure_stop" event. Used by those
	 * components that use a separate component to perform configuration and
	 * need to signal when de-configuration should be performed - usually after
	 * {@link #STOP_EVENT} and before {@link #AFTER_STOP_EVENT}.
	 */
	public static final String CONFIGURE_STOP_EVENT = "configure_stop";


	// --------------------------------------------------------- Public Methods

	/**
	 * Add a LifecycleEvent listener to this component.
	 *
	 * @param listener The listener to add
	 */
	public void addLifecycleListener(LifecycleListener listener);

	/**
	 * Get the life cycle listeners associated with this life cycle. If this
	 * component has no listeners registered, a zero-length array is returned.
	 */
	public LifecycleListener[] findLifecycleListeners();

	/**
	 * Remove a LifecycleEvent listener from this component.
	 *
	 * @param listener The listener to remove
	 */
	public void removeLifecycleListener(LifecycleListener listener);

	/**
	 * Prepare the component for starting. This method should perform any
	 * initialization required post object creation. The following
	 * {@link LifecycleEvent}s will be fired in the following order:
	 * <ol>
	 * <li>INIT_EVENT: On the successful completion of component
	 * initialization.</li>
	 * </ol>
	 *
	 * @throws LifecycleException if this component detects a fatal error
	 *                            that prevents this component from being used
	 */
	public void init() throws LifecycleException;

	/**
	 * Prepare for the beginning of active use of the public methods other than
	 * property getters/setters and life cycle methods of this component. This
	 * method should be called before any of the public methods other than
	 * property getters/setters and life cycle methods of this component are
	 * utilized. The following {@link LifecycleEvent}s will be fired in the
	 * following order:
	 * <ol>
	 * <li>BEFORE_START_EVENT: At the beginning of the method. It is as this
	 * point the state transitions to
	 * {@link LifecycleState#STARTING_PREP}.</li>
	 * <li>START_EVENT: During the method once it is safe to call start() for
	 * any child components. It is at this point that the
	 * state transitions to {@link LifecycleState#STARTING}
	 * and that the public methods other than property
	 * getters/setters and life cycle methods may be
	 * used.</li>
	 * <li>AFTER_START_EVENT: At the end of the method, immediately before it
	 * returns. It is at this point that the state
	 * transitions to {@link LifecycleState#STARTED}.
	 * </li>
	 * </ol>
	 *
	 * @throws LifecycleException if this component detects a fatal error
	 *                            that prevents this component from being used
	 */
	public void start() throws LifecycleException;

	/**
	 * Gracefully terminate the active use of the public methods other than
	 * property getters/setters and life cycle methods of this component. Once
	 * the STOP_EVENT is fired, the public methods other than property
	 * getters/setters and life cycle methods should not be used. The following
	 * {@link LifecycleEvent}s will be fired in the following order:
	 * <ol>
	 * <li>BEFORE_STOP_EVENT: At the beginning of the method. It is at this
	 * point that the state transitions to
	 * {@link LifecycleState#STOPPING_PREP}.</li>
	 * <li>STOP_EVENT: During the method once it is safe to call stop() for
	 * any child components. It is at this point that the
	 * state transitions to {@link LifecycleState#STOPPING}
	 * and that the public methods other than property
	 * getters/setters and life cycle methods may no longer be
	 * used.</li>
	 * <li>AFTER_STOP_EVENT: At the end of the method, immediately before it
	 * returns. It is at this point that the state
	 * transitions to {@link LifecycleState#STOPPED}.
	 * </li>
	 * </ol>
	 * <p>
	 * Note that if transitioning from {@link LifecycleState#FAILED} then the
	 * three events above will be fired but the component will transition
	 * directly from {@link LifecycleState#FAILED} to
	 * {@link LifecycleState#STOPPING}, bypassing
	 * {@link LifecycleState#STOPPING_PREP}
	 *
	 * @throws LifecycleException if this component detects a fatal error
	 *                            that needs to be reported
	 */
	public void stop() throws LifecycleException;

	/**
	 * Prepare to discard the object. The following {@link LifecycleEvent}s will
	 * be fired in the following order:
	 * <ol>
	 * <li>DESTROY_EVENT: On the successful completion of component
	 * destruction.</li>
	 * </ol>
	 *
	 * @throws LifecycleException if this component detects a fatal error
	 *                            that prevents this component from being used
	 */
	public void destroy() throws LifecycleException;

	/**
	 * Obtain the current state of the source component.
	 *
	 * @return The current state of the source component.
	 */
	public LifecycleState getState();

	/**
	 * Obtain a textual representation of the current component state. Useful
	 * for JMX.
	 */
	public String getStateName();

	/**
	 * Marker interface used to indicate that the instance should only be used
	 * once. Calling {@link #stop()} on an instance that supports this interface
	 * will automatically call {@link #destroy()} after {@link #stop()}
	 * completes.
	 */
	public interface SingleUse {
	}
}
